Many modern vehicles are equipped with some form of information display located either among the vehicle's instruments or in the vehicle's dashboard. A large quantity of information can be displayed, for example information about the operating condition of the vehicle, telephone numbers and navigation aids. It can happen that the driver is distracted by the information on the display and as a result looses concentration on the road. There are, in addition, several other devices in the modern vehicle that distract the driver, for example telephone and audio equipment. This can lead to the vehicle coming close to or crossing over one of the road's lane lines, for example, the centerlines and side lines of the road.
Even if the vehicle's deviation is small, this can disturb the drivers of other vehicles in the surrounding area. In the event of large deviations and/or deviations of longer duration, there is a risk that there may be an accident with serious consequences if, for example, the driver has fallen asleep.
There are known systems that alert the driver when he or she approaches or crosses over a lane line. Some systems also indicate in which direction the deviation occurs.
The use of one or more lamps to alert the driver is already known. Such a system shows warning lights from the side toward which the deviation occurs. If the deviation is large, several lamps can light or the intensity of the light can be increased. There are also systems where a lamp flashes and where the flashing frequency increases when the deviation increases.
JP 11126300 describes a method in which the system alerts the driver via a loudspeaker. The system alerts the driver by means of an audible signal from the side toward which the deviation occurs. For example, a warning sound is emitted from the right loudspeaker if the vehicle is too far toward the right. The intensity of the sound increases as the deviation increases. In addition, an image of a vehicle is shown on a display, with the color of the vehicle changing depending upon the size of the deviation.
EP 1235052 and JP 2001341599 describe systems that alert the driver by means of vibration at the driver's seat when the vehicle unintentionally changes lane.
These methods can work in most cases, but they have certain disadvantages.
One disadvantage is that lamps and audible signals must be modified to suit the surroundings. For example, a quiet audible warning system is not noticed if the driver is playing loud music or if the traffic noise is loud, while at the same time an audible warning signal must not be so loud that the driver is disturbed if it is quiet in the cab. The same applies for lamps that must be easily visible even if the driver views them against the light, while at the same time the lamps must not disturb the driver, for example when he is driving at night.
When the warning signals are given by means of lamps, it is also necessary to have an extra installation with lamps and cabling which is unnecessarily expensive.
Another disadvantage is that it is difficult to provide information about the size of the deviation, by means of lamps, audible signals or vibrations, that is easy to understand. As flashing frequency, light brightness, sound level, sound frequency and the like are relative concepts, it is difficult for a driver to interpret the size of the deviation. In many cases, the driver only perceives that the deviation is small or large.
Another disadvantage with certain known systems is that the warning signal is not simple and clear, and as a result, there can be a danger that the driver will miss the warning.